A variety of applications exist for precisely locating the source or radio waves such as radar transmitters. Conventional location techniques employ signal arrival time-difference and phase-difference at spatially separated low gain or so-called main beam receivers and require simultaneous illumination of the receivers by the target radar signal. However, the receivers must have sufficiently small angular separation relative to the radar to achieve simultaneous illumination, which is not always practical. In addition, the geometric dilution of precision increases as the separation of the receivers decreases. Thus, there remains a need for improved techniques and apparatus for detecting the source of radar and other radio wave transmission.